Pressure responsive cutout switch and the like



March 20, 1945. P O 2,371,648

PRESSURE RESPONSIVE CUTOUT SWITCH AND THE LIKE Filed Nov. 14, 1942 Inventor: Leslie C. Pierson,

His Attorn ey.

Patented Mar. 20, 1945 UNITED STATES PATENT OFFICE PRESSURE RESPONSIVE CUTOUT SWITCH AND THE LIKE Leslie 0. Pierson, Schenectady, N. Y., assignor to General. Electric Company, a corporation of New York The present invention relates to pressure respom ve cutout switches and like devices as may be used for connecting and disconnecting a power agency for driving a compressor in response to certain fluid pressure conditions in a chamber or consumer for receiving compressed medium discharged from the compressor.

The general object of my invention is to provide an improved construction of pressure responsive cutout switches and like devices which are moved in one direction, for example, to open an electric circuit for a power agency and moved in the opposite direction to close the circuit of such power agency at diiferent pressures.

For a consideration of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto in connection with the accompanying drawing.

In the drawing Fig. 1 illustrates a blower arrangement including a cutout switch in accordance with my invention; Fig. 2 is a sectional view of a cutout switch embodying my invention; Fig. ,3 is a section along line 3-3 of Fig. 2, Fig. 2 being a section along line 2--2 of Fig. 3; Fig. 4 is an exploded perspective view of certain parts of Fig. 2; and Fig. 5 illustrates a modification according to my invention.

The arrangement of Fig. 1 comprises a blower or centrifugal type compressor l0 having an inlet II and an outlet l2 connected to supply compressed air to a consumer or reservoir 13. The

compressor is driven by an electric motor l4 connected to a source or power line I5 by an electric circuit which includes a pressure responsive cutout switch It communicating through a pipe I! with the reservoir l3. The switch I6 is designed to open the motor circuit at a predetermined pressure in the reservoir [3 and to close the circuit after said pressure has dropped to a predetermined value. For example, the switch may be designed and adjusted to open the circuit of the motor H at a fluid pressure of 1000 pounds per square inch in the reservoir [3 and to close the circuit only after the pressure in the reservoir l3 has dropped to 800 pounds per square inch. Such operation is desirable in certain plants, especially on aircraft, to reduce to a minimum the closing and opening operations of the switch and the apparatus associated therewith, thereby to lengthen their life and to reduce the noise and other disturbances caused by the starting operations of the motor-operated blower. In other words, the switch l8 according to my invention reduces to a small number the starting and stopping operations of the motor-driven blower compared with a pressure switch actuated whenever the pressure drops slightly below normal pressure.

The cutout switch 16, as shown in Figs. 2, 3 and 4, comprises a housing 18 which forms a chamber I9 closed at its upper end by a plug 20 screwed into the housing and sealed thereto by a gasket 2|. The left-hand end of the housing forms a threaded, tubular extension 22 accommodating two terminals 23 and 24 supported on and electrically insulated from the housing by insulating material 25. The inner ends of the terminals are screwed into supports 26 and 21 for contacts 28 and 29 respectively. The contacts 28, 29 which preferably are made of silver are integrally united with the metallic supports 26, 21. The contact supports 26, 21 are insulated from the bottom of the housing by a plate 30 of insulating material and from the side wall of the housing by a sheet 3| of electrical insulating material. The terminals 23, 24 are electrically connected to the power line [5 and the motor 14 respectively, as shown in Fig. 1.

The bottom or lower wall portion of the housing 18 has a central differential bore 32 with a small diameter outer portion 33 and a. large diameter inner portion 34 forming ashoulder 35 between them. A differential piston or plunger 36 is slidably disposed in the differential bore 32 with its differential face engaging the shoulder 35 of the diiferential bore when in the outer end portion shown in Fig. 2. The inner portion of the .plunger 36 is provided with an extension 31 of electrical insulating material. This extension has a spherically-shaped head engaging a contactmaking and breaking disk or like member 38. The disk 38 in the present example is bimetallic, the upper portion consisting of copper and the lower portion or coating consisting of silver to assure a good electrical connection vbetween the contacts 28, 29.

The central portion 39 of the disk 38 forms a depression. The lower or concave-shaped surface of the central portion 39 engages the spherical end portion or head 31 of the plunger 36 and the upper or convex-shaped surface of the central portion 39 engages an insulating spring plate 40, which latter hasa central, substantially spherically-shaped depression 4| in contact with the central portion 39 of the contact-makin member 38. The spring plate 40 is biased downward by a compression spring 42 having a lower end located in a recess of the spring plate. The spring 2 is located in an annular recess 43 formed in the plug 20. The compression of the spring 42 may be va ied by the insertion or the removal of shims the housing. The casing chamber i9 is partly I filled with oil or like liquid 45. Finally, the plug 23 is assembled with the spring 42 and the spring plate 43 and screwed into the upper end of the housing.

The small diameter or outer portion of the differential plunger 36 has a rounded head or spherical end face 46 projecting below the small diameter bore 33 in the position shown in Fig. 2.

This rounded end portion of the differential plunger is sealed to the casing I8 by means of a flexible sealing disk ll made of a rubber-like oil resistant material such as neoprene. The sealing disk 51 is located in a central recess 48 in the bottom of the casing l8 and held in position by means of a ring 49 threaded into the recess 48.

In certain instances I have found it desirable to mold the sealing diaphragm 41 to the end of the differential piston 36 and the adjacent wall of the casing I8.

The cutout switch is simple in design and may be manufactured at comparatively low cost. The contact-making and breaking member, due to its spherical engagement with the head 31 and the depression in the spring plate 30, is self-aligning, that is, once the contact-making member is forced down into engagement with the contacts 28, 29 it will align itself automatically with the contact surfaces of the contacts 28, 29 and it will remain in this aligned position during subsequent movement of the plunger 36. The selfaligning feature of the contact plate 38 and certain other features of the switch are disclosed in and form part of the application of P. J. Schwarzhaupt et al., Serial No. 377,034, filed February 1, 1941. An important feature of my invention is the provision of a difierential plunger movably disposed in a differential bore and arranged to engage in one end position the shoulder formed by the differential bore bet'ween its large and small diameter portions 34 and 33 respectively.

'Other important features are the provision of means for hermetically sealing the outer end of the plunger to the switch casing and finally, the provision of a liquid, preferably a light oil, partly filling the contact chamber of the switch. If the switch is to be used as a pressure responsive switches in the arrangement of Fig. 1, the lower-central face of the sealing diaphragm 41 is exposed to the fluid pressure to be measured, that is, in response to which the switch is to be actuated. In the arrangement of Fig. 1 the switch I is connected to the pipe I! by means of an adapter 5|] which forms a conduit connection between the pipe I! and the opening of the ring 49. g

In the present example the plunger 36 abuts against the shoulder 35 of the differential bore in contact-closing position. Upon increase in pressure in the reservoir l3 the force acting against the lower face of the sealing disk 41 increases and as a certain pressure is reached in the reservoir l3, say 1000 pounds per square inch, the plunger 36 is moved upward to interrupt the connection between the contacts 28, 29. Upon subsequent decrease in pressure in the reservoir l3 to a predetermined value, for example 20%,

below the normal pressure of 1000 pounds per square inch in the reservoir l3 the plunger 35 is forced downward to permit bridging of the contacts 21, 28 by the contact plate 38.

One explanation for the pressure difference between the opening and closing action of the switch is that the differential piston in cooperation with the differential cylinder or bore formed by the casing act somewhat like a dashpot which has different restraining forces in the two directions of movement of the differential dashpot plunger. It takes a smaller force to move the plunger 35 upward in opening direction than it takes to move it downward into closing direction of the contacts. During upward or opening movement oil or like liquid contained in the contact chamber leaks down into the annular space created between the differential bore and the' differential plunger and, similarly, during closing movement oil contained in said annular space is forced back into the contact chamber along the small clearance formed by the sliding fit between the large diaphragm plunger part and the large diaphragm bore. It apparently takes a greater force to move the oil out of the annular space formed between the differential plunger and the differential bore than it takes for the oil to leak into such annular space.

In view of the different pressures necessary to effect closing and opening respectively of my improved pressure switch, such switch may be considered a dilierential pressure switch.

The modification shown'in Fig. 5 shows an arrangement in which a switch similar to that of Fig. 2 is used as a temperature responsive device or more specifically a differential temperature switch. The arrangement comprises a switch casing 5| corresponding to the casing l8 of Fig. 2 and forming a differential bore 52 for accommodating a differential plunger 53 corresponding to the plunger 36 of Fig. 2. In the position shown the plunger 53 has a differential face slightly spaced from the shoulder formed by the diiierential bore 52, thus constituting an annular space 54 filled with liquid 55.forced into said annular space from a contact chamber 56 corresponding to chamber 19 in Fig. 1. The lower end of the differential plunger 53 is spherical and sealed to the casing 5! by a flexible sealing disk 51 held in position by a ring 58 screwed into an opening in the casing 5|. The actuation in response to temperature changes is accomplished by the provision of known means for converting temperature changes into pressure changes. In the present example an adapter 59 is screwed into the lower central opening of, the casing 5| and connected to a pipe 60 which has a sealed end portion 6| located within a conduit or container 62 for conducting or containing a heated medium. The pipe 50 is partly filled with fluid. Thus, temperature changes of the medium contained in or conducted through the container 62 cause pressure changes of the fluid contained in the conduit 60. These pressure changes through the adapter 59 are communicated to the lower face of the sealing-disk 51 to cause movement of the differential plunger 53. Thus, my differential pressure switch or device also constitute or may readily be used as a differential temperature switch or device and when used as such a contact-making and breaking member or the like will be moved imo one end position upon the occurrence of a predetermined temperature condition and into another end position upon the occurrence of a predetermined lower temperature condition of a medium to be controlled.

Having described the method of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Pressure cutout switch comprising a housing forming a chamber and a differential bore.

chamber and secured to the casing, and a contact bridging disk for closing the contact carried by the plunger.

2. Pressure cutout switch comprising a casing forming a contact chamber and a differential bore through the bottom thereof, said bore having large and small diameter parts, a differential plunger having large and small diameter portions slidably disposed within the large and small diameter parts respectively of the bore and having an inner end portion projecting into the chamber and an outer end portion projecting out of the bore, means sealing the outer end portion to the bore, a contact-making and breaking device associated with the inner end portion,

means biasing the plunger into the bore, and liquid partly filling the chamber and adapted to leak along the plunger and to ill! the annular space formed upon movement of the plunger between the diflerential faces of the plunger and the bore.

3. Differential pressure device comprising a casing forming a chamber and a differential bore with a large and a small diameter part through a lower partof the casing, a differential plunger having a large and a small diameter portion slida'bly disposed in the respective parts of the bore,

spring means located in the casing for forcing the plunger into the bore, a flexible sealing disk for-sealing the outer end portion of the plunger element at one pressure -and disengaging such element at another pressure, said device comprising a casing forming a chamber and a differential bore through a lowerwall of the easposition.

ing, a differential plunger slidably disposed in the bore, the small diameter portion of the plunger having a spherical end face located substantially outside the bore in one end position, a flexible diaphragm sealing the spherical end face to the casing, means located in the chamber to bias the plunger into said end position, and liquid partly filling said chamber.

5. Differential pressure device comprising a casing forming a chamber and a differential bore through a lower wall thereof, said bore having an inner large diameter and an outer small diameter part, a differential plunger having large and small diameter portions slidably projecting through the corresponding parts of the bore, the small diameter part of the plunger having a spherical end face located substantially outside the bore in one end position of the plunger, a flexible diaphragm having a central spherical depression molded to said end face .to seal the plunger to the casing, means located in the chamber for biasing the plunger into the bore. said chamber being adapted to be initially filled with light oil in order to effect movement of the plunger into said end position at a pressure substantially lower than the pressure for efi'ecting movement of the plunger away from said end LESLIE C. PIERSON. 

